1. Field of the Invention
This invention relates to a paper-feed apparatus and method used in a facsimile apparatus, a copying apparatus, a printing apparatus, and the like, and more particularly to a friction paper-feed apparatus which is capable of preventing a paper-feed failure caused by a slippage made between a paper and a friction roller.
2. Discussion of the Background
A paper-feed function is an essential function in an information processing apparatus, such as, a facsimile apparatus, a copying apparatus, a printing apparatus, and so forth, wherein paper is handled as a medium for transferring information. A background art paper-feed apparatus applied in these conventional information processing apparatuses uses friction to transfer paper, and is therefore called a friction paper-feed apparatus.
The conventional friction paper-feed apparatus is widely known and used to transfer an original document for a reading operation of an apparatus having a reading function, such as, a facsimile apparatus, a copying apparatus, and so forth. As a basic configuration of the friction paper-feed apparatus for this case, the unit includes a paper input tray for holding the original document, a paper separation unit for separating a sheet of the original document to be transferred from other sheets of the original document, and a first friction paper-feed roller for transferring the separated sheet using friction. Further, the unit includes a first sensor for detecting a leading edge of the sheet to be transferred so as to determine a start time for a reading operation, a second friction paper-feed roller for further transferring the sheet during a time period of the reading operation, and a second sensor for detecting a trailing edge of the sheet to determine an end time of the reading operation.
Exemplary configurations of a friction feeding portion of the conventional friction paper-feed apparatus for transferring an original document for a reading operation are shown in FIGS. 8(a)-8(c). A type shown in FIG. 8(a) is called a "friction pad" apparatus and method, includes an input paper tray 201, sheets of an original document 202, a friction paper-feed roller 203, and a friction pad 204. In this configuration, a bottommost sheet of the original document 202 is pulled out by the friction paper-feed roller 203. This sheet then receives a pressure (i.e., a force), indicated by a letter F with an arrow in FIG. 8(a), from the friction pad 204 which increases friction between the friction paper-feed roller 204 and the sheet. Consequently, the friction paper-feed roller 204 of the friction pad method properly transfers a sheet of the original document in the reading operation.
Another conventional friction-feed device is shown in FIG. 8(b) and is called a friction roller apparatus and method and has a similar configuration to that in FIG. 8(a) except for a friction roller 304 which allows the friction paper-feed roller 303 to transfer a bottommost sheet and stops extra sheets attached to the bottommost sheet by stopping rotation by a function of a torque limiter. In this way, the friction paper-feed roller of the friction roller method can properly transfer a sheet of an original document for a reading operation.
Another conventional device is shown in FIG. 8(c) and is called a forward-and-reverse roller. This device has a similar configuration to that of FIG. 8(b) except for use of a forward-and-reverse roller 404 which normally rotates clockwise to feed a bottommost sheet and starts to rotate counter-clockwise when extra sheets are attached to the bottommost sheet, so that these extra sheets can be fed in reverse. In this way, the friction paper-feed roller of the forward-and-reverse roller can properly transfer a sheet of an original document for a reading operation.
The background art friction paper-feed apparatuses and methods are widely used to transfer blank paper for a printing operation of an apparatus having a printing function, such as, a facsimile apparatus, a copying apparatus, a printing apparatus, and so forth. A basic configuration for the friction paper-feed apparatuses for transferring a blank paper is similar to that of the above-mentioned units when used in a reading operation. More specifically, the units generally include a blank paper cassette for holding a large number of sheets of blank paper, a separation unit for separating one sheet of blank paper from the blank paper cassette, and a first friction paper-feed roller for transferring the separated sheet of blank paper using friction. Further, the units include a first sensor for detecting a leading edge of the sheet so as to determine a start time of a printing operation, a second friction paper-feed roller for further transferring the sheet during a time period of the printing operation, and a second sensor for detecting a trailing edge of the sheet so as to determine an end time of the printing operation.
Exemplary configurations of a friction feed portion of the above-mentioned friction paper-feed apparatus for transferring blank paper for a printing operation are shown in FIGS. 9(a)-9(c). As shown in FIG. 9(a), a friction pad device and method includes an input paper tray 501, sheets of an original document 502, a friction paper-feed roller 503, and a friction pad 504 including a spring for providing a pressure. In this configuration, a topmost sheet of the original document 502 is pulled out by the friction paper-feed roller 503 and then receives a pressure, indicated by a letter "F" and an arrow in FIG. 9(a), from the friction pad 504 increasing friction between the friction paper-feed roller 504 and the sheet. As a result, the friction paper-feed roller 504 can properly transfer blank paper for a printing operation.
As shown in FIG. 9(b), another friction roller and method has a similar configuration to that of FIG. 9(a) except for a friction roller 604 which allows the friction paper-feed roller 603 to transfer a topmost sheet and stops extra sheets attached to the topmost sheet by stopping rotation as a function of a torque limiter mounted in the friction roller 604. In this way, the friction paper-feed roller 603 of the friction roller method can properly transfer blank paper for a printing operation.
Another type is shown in FIG. 9(c) and is called a forward-and-reverse roller. This forward-and reverse roller has a similar configuration to that of FIG. 9(b) except a forward-and-reverse roller 704 is used and which normally rotates clockwise to feed a topmost sheet and starts to rotate counter-clockwise when extra sheets are attached to the topmost sheet, so that these extra sheets can be fed in reverse. In this way, the device of FIG. 9(b) using the friction paper-feed roller 703 can properly transfer blank paper for a printing operation.
Still another type of device which is capable of feeding a blank sheet from rolled paper using a friction paper-feed roller is similar to that mentioned above is also known as the friction paper-feed apparatus (not shown in the figures).
However, as identified by the present inventor, the above-mentioned configurations of the friction paper-feed method and apparatus for both the reading and printing operations share a common problem of a paper-feed failure caused by a slippage between a sheet of paper being transferred and a friction paper-feed roller. Specifically, such a paper-feed failure typically occurs when a sheet of paper is continuously transferred through a long and bending path. For example, an operation of transferring a sheet of paper in a reading operation of a facsimile apparatus may cause a paper-feed failure in a long and bending path, for example, between the paper tray and the position of the first sensor or the registration sensor. This slippage, as identified by the present inventor, is because frictional forces are produced at various regions, for example, between the sheet and an adjacent sheet, the sheet and four inside surfaces of the path, and so on, by the moving paper sheet, and, specifically, the friction at a bending or a narrowing portion in the path may become greater than one generated between the sheet and the friction paper-feed roller.
More specifically, frictional forces may usually occur at both top and bottom sides of a sheet of paper when a friction paper-feed roller transfers a topmost sheet from one of plural sheets of paper. One of the frictional forces may occur at the top side of the moving sheet as the friction paper-feed roller rotates while contacting the sheet. At the same time, another frictional force may occur at the bottom side of the moving sheet since the moving sheet contacts a top surface of an adjacent sheet. Therefore, the friction paper-feed roller is required to have a rougher surface, as compared with a surface of the adjacent sheet, so as to generate a frictional force with the top surface of the sheet greater than another frictional force generated at the bottom side of the sheet.
If frictional coefficients at the above-mentioned top and bottom sides of the sheet are represented by .mu..sub.1 and .mu..sub.2 respectively, the relationship between .mu..sub.1 and .mu..sub.2 is defined as
.mu..sub.1 and .mu..sub.2 =0 PA1 .mu..sub.1 and .mu..sub.2 &gt;0. PA1 .mu..sub.2 &gt;.mu..sub.1 =0. PA1 .mu..sub.2 &gt;.mu..sub.1 &gt;0.
when the friction paper-feed roller is not driven. However, these frictional coefficients may change when the friction paper-feed roller starts to rotate. More specifically, in order to feed the sheet of paper, the relationship between .mu..sub.1 and .mu..sub.2 is required to become
If the sheet thus starts to move and is then given a disturbing (opposing) force against such a movement by any accidental reason as mentioned below, the moving sheet may stop but still maintain contact with the rotating friction paper-feed roller. Such events tends to happen when the moving sheet goes into a bending or a narrowing portion, for example, of the transferring path. In these cases of slippage, the relationship between .mu..sub.1 and .mu..sub.2 changes into
Once the friction paper-feed roller begins to slip or a paper-feed failure occurs, it is difficult to make the roller re-grip the paper because the friction coefficient .mu..sub.1 becomes null. As a result of the paper-feed failure, the sheet of the original document may be damaged in a serious manner since the friction paper-feed roller continues to rotate and rub the surface of the jammed sheet.
In addition, even if the jammed sheet is not damaged during the above-mentioned accidental slippage or a paper-feed failure, the surface of the jammed sheet may become relatively more smooth since the rotating friction paper-feed roller rubs a surface of the jammed sheet. In this case, .mu..sub.1 becomes relatively smaller and the relationship between .mu..sub.1 and .mu..sub.2 may also change into
After that, the friction paper-feed roller may always slip on this particular sheet having a relatively smoother surface and cause a paper-feed failure during future operations.
As mentioned above, as determined by the present inventor, the cause of the paper-feed failure on the paper-feed apparatus using the friction paper-feed roller is a slippage which may bring about serious damage to an original document. In this circumstance, however, a problem is that there is no friction paper-feed apparatus which is capable of preventing, detecting, and recovering from a paper-feed failure so as to handle an original document in a secure manner.